Protecting Boiler Feed Water Pump Against Cavitation Through Applied Mathematical Approach

Boiler Feed Water Pumps play a crucial role in the Power Generation Blocks (PGBs) Unit at Jazan Refinery Complex (JZRC). Frequent pump trips due to cavitation have resulted in significant financial losses and operational disruptions. This manuscript introduces an innovative exponential solution which is mainly an equation to enhance pump protection against cavitation. This equation utilizes Factory Acceptance Tests performance curves values to precisely describe the pump's behavior, directly addressing the cavitation phenomenon. The combination of this logic protection and the derived equation has been filed for a U.S. patent. Furthermore, this innovative approach has already been successfully implemented on 16 out of 20 Boiler Feed Water pumps at JZRC during PGB-1/2/3/4 Commissioning and Startup (CSU), with ongoing implementation on the remaining four pumps at PGB-5. The intention of developing a better approach to protect the Boiler Feed Water (BFW) pumps against cavitation was an initiative to consider a dynamic model instead of fixed value for Net Positive Suction Head Available - NPSHA (14.7 m) based on 1 m separation margin respect to Net Positive Suction Head Required - NPSHR (13.7 m) @ rated flow provided by Pump Manufacturer, which was found very conservative protection at flowrates less than rated flow where NPSHR is less than 10 m and pump not well protected at flowrates exceeding the rated flow where NPSHR is expected to be above 20 m. The dynamic model of protection, implemented by NPSH margin equation, has been applied successfully at Power Block Power Generation Units to avoid unnecessary trips at flowrates below rated flow and protect the pumps effectively when running at flowrates above rated flow. NPSH margin ESD trip @ 1 m (decreasing) replaced the NPSHA trip set on 14.7 m (decreasing) to enhance the pumps reliability and availability, if the sister pump was unable to kick-in, leading to trip the Gas Turbine and loss of 220 MW of power generation. Each power block has 02 gas turbines with 02 HRSG's and 01 steam turbine. Each HRSG has associated 02 BFW pumps, one running while the other is on hot standby. [Figure 1]